A closed-loop approach for enhanced biodiesel recovery from rapeseed biodiesel-based byproducts through integrated glycerol recycling by black soldier fly larvae

Abstract

The present study evaluated an innovative zero-waste approach for efficient recycling of byproducts from rapeseed-based biodiesel industry including lipid-free rapeseed cake (RSC) and waste glycerol by black soldier fly larvae (BSFL). RSC showed high organic matter and protein contents of 92.7 dw% and 32.1 dw%, respectively. Therefore, it was utilized as the main feed source for BSFL rearing, while waste glycerol was supplemented at different concentrations (0–10%, w/w). Application of 5.0% waste glycerol significantly enhanced larval biomass gain rate and areal productivity by 13.0% and 17.2%, respectively, over the control. Interestingly, lipid content also increased by 25.9% over the control. The study suggested a synergistic action in the mixture, where RSC is digested to achieve the growth and development, while waste glycerol can be integrated directly into fatty acid biosynthesis pathway to accumulate lipids. In addition to being a carbon source, morphological examination and FTIR analysis showed that waste glycerol has the potential to penetrate RSC biomass fibers easing its decomposition. Overall, the highest recorded fatty acid methyl esters (FAMEs) productivity of 98.0 mg m−2 was recorded in BSFL treated with 5.0% waste glycerol, which represented 57.7% higher than the control. Comparing to rapeseed biodiesel, saturated fatty acids proportion in the BSFL-based FAMEs at all studied treatments was much higher, leading to 11.9–12.9% higher cetane number. In conclusion, findings of this study provide new insights to BSFL as a promising mini-livestock for biodiesel production through innovative recirculation route of biodiesel byproducts towards waste reduction and sustainable development.